JP2867343B2 - Electrorheological fluid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECT OF THE INVENTION INDUSTRIAL APPLICATION FIELD The present invention relates to an electrorheological (Electro Rh.
eological) Fluids, especially non-aqueous electro-rheological fluids that do not substantially contain water, and are related to electro-rheological fluids with improved stability against components extracted from rubber, resin, etc., such as engine mounts, shock absorbers, and valves Used for electrical control of mechanical devices such as actuators and clutches.

2. Description of the Related Art A phenomenon in which the apparent viscosity of a fluid is greatly changed by the application of an electric field has long been known as the Winslow effect.
The early electrorheological fluids consisted of starch or starch dispersed in mineral oil or lubricating oil, which was sufficient for recognizing the importance of the electrorheological effect, but lacked reproducibility.

In order to obtain a fluid having a high electrorheological effect and good reproducibility, many proposals have been made so far, mainly on fine powder used as a dispersed phase. For example, highly water-absorbing resin particles having an acid group such as polyacrylic acid (JP-A-53-93186), ion-exchange resins (JP-B-60-31211), and alumina silicate (JP-A-62-95397) are known. Had been.

All of these electrorheological fluids are made of hydrophilic solid fine powder containing water and dispersed in an insulating oily medium. When a high voltage is applied from the outside, the fine powder is polarized by the action of water. It is said that the polarization increases crosslinks between the particles in the direction of the electric field, thereby increasing the viscosity.

However, in electrorheological fluids using these water-containing fine powders, the operating temperature is limited to prevent evaporation or freezing of water, the current increases significantly due to temperature rise, the stability is insufficient due to the transfer of water, or high voltage is applied. There are many problems such as dissolution of the electrode metal at the time, which is a major obstacle to the practical use of the electrorheological fluid.

In recent years, non-aqueous non-aqueous electrorheological fluids using ferroelectric substances and semiconductor particles have been proposed. For example, a fluid using organic semiconductor fine particles such as polyacenequinone (JP-A-61-216202), and a dielectric fine particle in which a conductive thin-film layer is formed on the surface of organic solid particles and an electrically insulating thin-film layer is further formed (JP-A-61-216202) 63-97694).

Non-aqueous electrorheological fluids are greatly expected to overcome various deficiencies due to the presence of water in conventional hydrous electrorheological fluids, and much research has been conducted.

The present inventors have also conducted research in this direction and have found that carbon fine powder having optical anisotropy exhibits an excellent electrorheological effect in a non-aqueous system (Japanese Patent Application No. 63-212615).

However, even with these non-aqueous electrorheological fluids, there is a new problem that is not present in conventional electrorheological fluids containing water, and it has been clarified that their applications are limited.

[Problem to be Solved by the Invention] The new problem is that when a non-aqueous electrorheological fluid is used in a mechanical device including rubber, resin, or the like as a component, its viscosity in an electric field-free (initial viscosity) ) Gradually increases, which causes a problem of greatly deteriorating the characteristics of the mechanical device. Such an increase in the initial viscosity is a phenomenon that cannot be seen in the conventional hydrous electrorheological fluid (see Reference Example described later), but has been found to be a problem common to nonaqueous electrorheological fluids. .

The present inventors have found that a viscosity increase that occurs when a non-aqueous electro-rheological fluid is used in a mechanical device including rubber, resin, or a composite material thereof as a component, which was not found in a hydrous electro-rheological fluid. As a result, it was found that components added to rubber, resin and the like were gradually extracted into the electrorheological fluid, and that the extracted components caused a rise in viscosity and a change in the initial characteristics, and the measures were intensively studied.

In general, a low-polarity compound is used as an insulating oil used for an electrorheological fluid in order to satisfy required electric characteristics. When a component different from the insulating oil is extracted into the insulating oil, the viscosity characteristics of the insulating oil change. This change in the viscosity characteristic depends on the extracted component, and in the case of the extracted component having a higher viscosity than the insulating oil, the viscosity of the insulating oil is increased. Further, when a component that is solid at room temperature has a slightly different solubility constant (SP value) from that of insulating oil, the insulating oil may change into a butter-like shape even if a small amount is extracted.

Generally, various compounds are added to rubber, resin, or a composite material thereof for the purpose of preventing deterioration and improving other properties in practical use. In addition to these additional components, rubber,
Low-molecular-weight unreacted substances contained in the resin or the polymer constituting these composite materials may be extracted into the insulating oil. Therefore, when using an electrorheological fluid in a mechanical device containing rubber, resin, or a composite material of these as a component,
The insulating oil used in the electrorheological fluid extracts rubber, resin, or components contained in these composite materials, and the viscosity characteristics change.

In water-based electrorheological fluids, powders having a high content of oxygen, which is an atom having high affinity for water, such as aluminum silicate, are generally used because water must be adsorbed (Japanese Patent Laid-Open No. 95397/1987). And 1-2 inside or outside of this powder
The electrorheological effect is exhibited by 5% by weight of highly polar water, but the effect of this water is not only to bring out the electrorheological effect, but also to eliminate the cause of the viscosity increase. Was found.

As an example, the case where an electrorheological fluid is used in a mechanical device containing rubber as a constituent element will be described. Compounds that become solid at room temperature, such as wax contained in rubber, are mostly polymers, but they are When extracted by the less polar insulating oil used in the fluid, if water is not present, the less polar wax, which is an extractable component, will have sufficient molecules to spread because the less polar insulating oil is a good solvent. It will be in a state where Further, since the wax is a solid at room temperature, a part thereof crystallizes to form a pseudo-crosslinking point, thereby increasing the viscosity.

However, if a highly polar molecule such as water is present, the polymer chain becomes charged, and the extended molecule shrinks as if it were in a poor solvent, forming a pseudo-crosslinking point. Precipitates. Therefore, the change in initial viscosity was slight and did not cause any problem.However, in the case of a non-aqueous electrorheological fluid, since water was not added, the wax contained in the rubber was extracted at 0.5% by weight or less in the fluid. Even if it is done, it becomes butter-like, and the initial viscosity is greatly increased, which is a practical problem.

The present invention has been made in order to solve the problems peculiar to such non-aqueous electrorheological fluids, and has an object to solve the problem even when used in a mechanical device used in contact with rubber or resin. An object of the present invention is to provide an electrorheological fluid with little change and high practicality.

B. The non-aqueous electrorheological fluid of the present invention comprises a carbonaceous fine powder having a water content of less than 1% by weight dispersed in an electrically insulating oily medium. A fluid, ethylene glycol,
0.01% by weight to 10% by weight of a compound having a hydrophilic group selected from the group consisting of polyethers composed of triethylene glycol or polyethylene glycol, silicones modified with ethylene oxide or propylene oxide, and polymers composed of liquid polymethacrylate It is characterized by containing the following.

 Hereinafter, the present invention will be described in detail.

The nonaqueous electrorheological fluid to which the present invention is applied is obtained by dispersing a carbonaceous fine powder having a water content of less than 1% by weight in an electrically insulating oily medium. It does not require the intended addition of water.

Generally, silicone oil,
Although mineral oil, transformer oil, paraffin oil, halogenated aromatic oil and the like are used, the present invention is effective even when any insulating oil is used, and the type of oil is not particularly limited.

The type, particle size, and composition of the carbonaceous fine powder used as the dispersion layer is not limited as long as the powder exhibits excellent electrorheological effects when water is less than 1% by weight, preferably 0.5% by weight or less.

The carbon fine powder suitable as a dispersed phase of the non-aqueous electrorheological fluid of the present invention will be further described.
% By weight, particularly preferably 90 to 95% by weight
It is. The C / H ratio (carbon / hydrogen atom ratio) of the carbonaceous fine powder is preferably from 1.2 to 5, particularly preferably from 2 to 5.
4 things.

Specifically showing the carbonaceous fine powder having the C / H ratio,
Coal tar pitch, petroleum pitch, finely crushed pitch obtained by pyrolyzing polyvinyl chloride, etc., fine powder consisting of various mesophases obtained by heat treatment of those pitch or tar components, that is, formed by heating Optically anisotropic microspheres (spherulites or mesophase microspheres)
Powder obtained by dissolving the pitch component in a solvent and fractionating it, further pulverized, and the pitch raw material is subjected to heat treatment to form a bulk mesophase (for example,
So-called low-temperature treated carbon fine powder, such as finely ground powder, finely ground partially crystallized pitch, or carbonized thermosetting resin such as phenolic resin at low temperature. And further pulverized coals such as anthracite and bituminous coal and heat-treated products thereof; hydrocarbon-based polymers such as polyethylene, polypropylene or polystyrene; and chlorine-containing polymers such as polyvinyl chloride or polyvinylidene chloride. And carbon spheres obtained by heating the mixture under pressure, or carbon spheres obtained by pulverizing the same, or those obtained by pulverizing the same.

The compound having a hydrophilic group used in the present invention is a compound in which a part or the whole of a molecule is constituted by a hydrophilic functional group, and can be expressed by an HLB value expressing the characteristics of a surfactant. The value should be 0.003 or more,
The compound is preferably 0.03 or more, and more preferably 0.2 or more and 20 or less.

Examples of the compound having an atomic group constituting such a hydrophilic group include ethylene glycol, polyethers composed of triethylene glycol or polyethylene glycol, silicones modified with ethylene oxide or propylene oxide, and polymers composed of liquid polymethacrylate. I can give it.

One or more additives selected from these compounds are added to the nonaqueous electrorheological fluid in an amount of 0.01% by weight or more and 10% by weight or less, preferably 0.01% by weight or more and 2% by weight or less.

As a compound having a hydrophilic group, petroleum sulfonate, a compound containing an ionic group such as an oil-soluble sulfonate such as calcium dodecylbenzenesulfonate also has the same effect of suppressing the increase in viscosity as in the present invention, but non-ionic It is preferable to select a compound having a property because the influence on the current value when a high voltage is applied can be reduced.

Regarding the amount of addition, when addition of 10% by weight or more is performed, even if the increase in viscosity can be suppressed, the current value increases when a voltage is applied, which is not preferable. The minimum amount required to suppress a rise in viscosity is preferred. For these reasons, the upper limit is 10% by weight, and preferably, the addition of 2% by weight or less reduces the influence on the current value.

The method of addition may be either one or a mixture of the above additives in the insulating oil in advance, or the addition of the electrorheological fluid immediately after production, and the addition method is not particularly limited. In order to obtain the effects of the present invention, the compound described in the present invention may be added to the non-aqueous electrorheological fluid in the amount described in the present invention, and is brought into contact with rubber, resin, and other general plastics. When using a fluid
It is possible to suppress an increase in viscosity due to the extracted component.

Hereinafter, embodiments and effects of the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Carbonaceous powder having an average particle diameter of 3 microns (carbon content: 93.78% by weight, C / H ratio: 2.35, mesophase carbon produced from coal tar pitch as a raw material by heat treatment in a nitrogen stream)
Oxygen atom content 0.8% by weight, water content 0.2% by weight) 100g
Is replaced by silicone oil (TSF451-1 manufactured by Toshiba Silicone Co., Ltd.)
0) Dispersed in 190 g to produce an electrorheological fluid. As a compound having a hydrophilic group, 0.7 g of silicon modified with ethylene oxide (HLB value = 2: silicon surfactant FZ2171 manufactured by Nippon Unicar Co., Ltd.) was added to 100 g of the fluid to obtain an electrorheological fluid of the present invention. .

FIG. 1 shows the voltage applied to an electrorheological fluid without addition of ethylene oxide-modified silicon (□: conventional technology) and an electrorheological fluid to which ethylene oxide-modified silicon is added (+: the present invention), and a change in viscosity accompanying the voltage. . In FIG. 1, the horizontal axis represents the applied voltage (KV), and the vertical axis represents the viscosity (P: poise) of the electrorheological fluid.

As is clear from FIG. 1, the □ mark and the + mark completely overlap, and the addition of the modified silicon does not affect the electrorheological effect. In addition, the current value of the electrorheological fluid to which the modified silicon was added when the 2 KV voltage was applied was 0.5 mA, which was the same as the case without the addition.

To the electrorheological fluid to which the modified silicon was added, the rubber having the composition shown in Table 2 was added by the same weight as the electrorheological fluid, and
Extraction was performed at 0 ° C. for 3 days. When the initial viscosity was measured before and after the rubber extraction, no significant change was observed as shown in Table 1 and the electroviscous effect was not affected.

[Comparative Example 1] In the electrorheological fluid to which the modified silicon was not added as shown in Example 1, the rubber having the composition shown in Table 2 was added in the same weight as the electrorheological fluid, and extraction was performed at 100 ° C for 3 days. . Before and after the rubber extraction, the initial viscosity changed from 0.8P to 3.0P as shown in Table 1.

From Example 1 and Comparative Example 1, the effect of adding the compound having a hydrophilic group is clear.

Example 2 As an additive, a mixture of modified silicon having the same HLB value of 2 as used in Example 1 and tetraethylene glycol at a ratio of 5: 3 was added at 0.8% by weight to the electrorheological fluid. Except for the above, an electrorheological fluid was manufactured in the same manner as in Example 1.

In the same manner as in Example 1, the rubber having the composition shown in Table 2 was added in the same weight as the electrorheological fluid, extraction was performed at 100 ° C. for 3 days, and the initial viscosity was measured before and after rubber extraction. As a result, the fluid had a significantly small change in the initial viscosity before and after the rubber extraction as compared with the case of no addition.

[Example 3] A liquid polymethacrylate surfactant (Acryl 806 manufactured by Sanyo Chemical Co., Ltd.) was used as an additive for an electrorheological fluid.
An electrorheological fluid was produced in the same manner as in Example 1 except that 0.5% by weight was added, and the electrorheological effect was measured before and after rubber extraction in the same manner as in Example 1. The results shown in Table 1 were obtained. No significant change in initial viscosity was observed.

[Reference Example] 40 g of 3A-type crystallized zeolite powder having an average particle size of 1 μm (manufactured by Union Showa Co., Ltd .: water content: 4.4% by weight) was dispersed in 90 g of silicone oil (TSF451-10 manufactured by Toshiba Silicone Co., Ltd.). This produced an electrorheological fluid.

To this electrorheological fluid, the rubber having the composition shown in Table 2 was added in the same amount as the electrorheological fluid, and extraction was performed at 100 ° C. for 3 days. When the initial viscosity was measured before and after the extraction of the rubber, no significant change was observed as shown in Table 1 and the electroviscous effect was not affected.

From this reference example, it was shown that the compound having a hydrophilic group described in the present invention was not required in the aqueous electrorheological fluid.

C. Effects of the Invention A non-aqueous electrorheological fluid with little change in characteristics and high practicality can be obtained even when used in a mechanical device used in contact with rubber or resin.

[Brief description of the drawings]

FIG. 1 shows the applied voltage to an electrorheological fluid without ethylene oxide-modified silicon (□: conventional technology) and an electrorheological fluid to which ethylene oxide-modified silicon was added (+: invention), and a change in viscosity accompanying the voltage. FIG.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C10M 155/02 C10M 155/02 159/12 159/12 // C10N 40:14 (56) References JP-A-2-91194 ( (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C10M 125/02 C10M 129/16 C10M 145/28 C10M 159/12 C10M 155/02 C10M 129/18 C10M 145/14 C10N 40 :14

Claims (1)

(57) [Claims] 1. An electrorheological fluid in which a carbonaceous fine powder having a water content of less than 1% by weight is dispersed in an electrically insulating oily medium, wherein said polyrheological fluid comprises ethylene glycol, triethylene glycol or polyethylene glycol. It contains a compound having a hydrophilic group selected from the group consisting of ethers, silicones modified with ethylene oxide or propylene oxide, and a polymer composed of liquid polymethacrylate in an amount of 0.01% by weight or more and 10% by weight or less. Non-aqueous electrorheological fluid.